46. mud volcanic samples in the context of the mediterranean ridge

Robertson, A.H.F., Emeis, K.-C., Richter, C., and Camerlenghi, A. (Eds.), 1998Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 160

46. MUD VOLCANIC SAMPLES IN THE CONTEXT OF THE MEDITERRANEAN RIDGE MUD DIAPIRIC BELT1

Grigorii G. Akhmanov2 and John M. Woodside3

ABSTRACT

Mud volcanism on the Mediterranean Ridge has been the object of intensive investigation during Training ThroughResearch (TTR) expeditions in 1993, 1994, and 1995 (Gelendzhik and Professor Logachev cruises). As a result, a large data-base has been compiled on the lithology of mud volcano deposits exposed on the seafloor.

The Ocean Drilling Program (ODP) holes that were drilled during Leg 160 within the Olimpi Area, the most studied muddiapiric area of the Mediterranean Ridge, have allowed us for the first time to look deeper into the mud volcanoes and to ana-lyze some peculiarities of their development since the Pliocene.

The composition of buried mud breccias that were recovered during Leg 160 was found to be rather typical of the Olimpiarea, as determined from the earlier TTR investigations. Significant differences between buried breccia and mud brecciaexposed on the seafloor were not observed. Most of the mud breccia clast types previously described for exposed mud brecciaflows of the Olimpi area were found in the ODP samples. No new types were observed in the buried and older mud breccias.

Mudstones are prevalent among rock fragments of the mud breccia samples recovered by ODP as well as in exposed Olimpimud breccia. Micrites, fossiliferous micrites, and packed biomicrites are as widespread among lithoclasts of the limestonegroup as in the youngest mud breccia flows. The different sandstone fragments observed in the ODP mud breccia samples cor-respond to the subfeldspathic lithic wackes and lithic arenites previously described from the Olimpi area. The crystalloclastshave all resulted from disintegration of different rock fragments within the mud breccia. The set of crystalloclasts correspondscompletely to component compositions of the lithoclasts. The Olimpi mud breccia matrix examined in both Leg 160 samplesand TTR samples is similar and mainly composed of smectite and mixed-layered (illite/smectite with prevalent smectite layers)clay minerals (40%−65%), kaolinite (15%−30%), and illite (10%−30%). The lack of significant downhole variation in mudbreccia composition suggests that the source formations for the Olimpi mud breccia have not changed since at least the latePliocene.

Comparisons of the compositions of the Olimpi mud breccia (on the basis both of ODP and previous data) with mud brec-cias from other known diapiric area on the Mediterranean Ridge exhibit some differences. The differences reflect peculiaritiesof source formation lithology and structural tectonic setting of mud volcanoes in different areas of the Eastern Mediterranean.There are also common features of the Mediterranean mud breccia, which indicate that some common sedimentary seriesextend through the whole Eastern Mediterranean.

INTRODUCTION

Mud volcanism on the Mediterranean Ridge has attracted the at-tention of scientists for almost 20 yr, since 1978, when the first Med-iterranean mud diapir was discovered west of Crete (Cita et al.,1981). Since then, intensive investigation of these phenomena has re-sulted in the discovery of numerous new mud volcanoes on the crestof the Mediterranean Ridge (Limonov et al., 1996) (Fig. 1). As a re-sult, a large data base has been compiled on the lithology of mud vol-cano deposits that are exposed on the seafloor or overlain by a thinveneer of Holocene ooze (see Cita et al., 1996, for a review and rele-vant references). Ocean Drilling Program (ODP) holes drilled duringLeg 160 were within the most studied mud diapiric area of the East-ern Mediterranean and have allowed us for the first time to look deep-er into the mud volcanoes and to analyze some peculiarities of theirdevelopment since the Pliocene. In this paper, we report the results ofan investigation of the mud breccia samples from the Milano andNapoli mud volcanoes drilled during Leg 160. These data are com-pared with those from studies of large volumes of mud breccia col-lected during UNESCO Training Through Research (TTR) expedi-tions to the mud volcano fields on the Mediterranean Ridge in 1993,

1Robertson, A.H.F., Emeis, K.-C., Richter, C., and Camerlenghi, A. (Eds.), 1998.Proc. ODP, Sci. Results, 160: College Station, TX (Ocean Drilling Program).

2Faculty of Geology, Moscow State University, Moscow, Russia.3Correspondence author: Faculty of Earth Sciences, Free University, De Boelelaan

1085, 1081 MV Amsterdam, The Netherlands. [email protected]

1994, and 1995 (Gelendzhik and Professor Logachev cruises). Thus,the ODP data are placed in their regional context and linked with theODP site survey data obtained during the TTR Program. The aimsand methodology of the research were the following:

1. recognition of the main mud breccia types on the basis of theirstructural and textural characteristics and interpretation of pe-culiarities of genesis of each type;

2. determination of mud breccia composition;3. comparison of the compositions of the Olimpi mud breccia (on

the basis of both ODP and previous data) with mud brecciasfrom other known diapiric area on the Mediterranean Ridge;

4. description of lithological and fabric variations of the mudbreccia sampled downhole, which are presented in verticalsection.

MATERIALS AND METHODS

A lithologic study of 37 samples of mud breccias and pelagic sed-iments from Sites 970 (Milano mud volcano) and 971 (Napoli mudvolcano) was performed in the laboratories of Moscow State Univer-sity. To identify the composition and structural and textural features,thin-section samples were examined under polarizing microscope.The core descriptions carried out on board during Leg 160 (Emeis,Robertson, Richter, et al., 1996) also provided the support for struc-tural investigations and interpretation of data.

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mailto:[email protected]

G.G. AKHMANOV, J.M. WOODSIDE

Figure 1. Location of the Mediterranean Ridge mud volcanoes (isobaths every 1000 m). See Figure 2 for detailed position of the mud volcanoes of the Olimpi/Prometheus 2 Area.

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Investigation of mud breccia composition is mainly based oncomparison with data previously obtained from this area (Akhmanov,1996), when there was an opportunity to examine large amounts ofmud breccia in detail and to study much larger clasts. Using charac-teristics such as structure, texture, composition, and lithology, threemain types of mud volcanic deposits were defined for the samples re-covered at the ODP sites. Lithological and fabric variations of thesampled mud breccia with depth below the seafloor were then con-sidered.

The principal clay mineral composition of matrix from buriedmud breccia was identified on the basis of X-ray analysis for compar-ison with data obtained from mud breccia flows exposed on the sea-floor.

MUD BRECCIA LITHOLOGY

The term mud breccia lithology as used here encompasses (1)mud breccia composition (including mud clast lithologies and mudbreccia matrix), and (2) sedimentary structures of the mud volcanicdeposits.

Mud Breccia Composition

Mud volcanic deposits are represented by a very complex mixtureof material from the sedimentary successions through which the mudvolcanoes erupted. Mud breccia, therefore, provides important infor-mation about the composition of the deep-seated formations of theMediterranean Ridge. In studying the mud breccia, we deal with frag-ments of rocks that were deposited millions of years ago, subsequent-ly buried, and are now situated at depths up to a few kilometers (Ca-merlenghi et al., 1995).

598

Mud breccia consists of a clayey and silt-sized matrix with abun-dant coarser clasts of terrigenous and biogenic material, and clay-stone fragments that are more consolidated than the matrix.

Mud Breccia Clast Lithologies

The clasts from Leg 160 samples can be divided into severalgroups: lithoclasts (fragments of different rocks), crystalloclasts(grains of minerals), and bioclasts (foraminifers, shell fragments,etc.). Fragments of mudstones predominate within the lithoclasts.They are tabular or bladed, very thinly laminated, and soft. The shapeand structure of some mudstone fragments imply plastic deformationof the fragments within the mud breccia. The size of mudrock frag-ments varies from 0.5 to 10 mm. Clay particles commonly show strictorientation that results in almost simultaneous extinction in the entirethin section of fragment.

Fragments of micritic limestones are abundant. They are massive,structureless, equant, rounded, and sometimes clay rich as well asrich in organic matter, and range in diameter from 1 to 3 mm. Fossil-iferous micrites are composed of Globigerina in a micritic calcite ma-trix with a clay admixture. Fragments of packed biomicrites werealso observed in several of the samples studied.

Siltstones, fine-grained sandstones with a clayey matrix, and fine-grained sandstones with calcite cement are also present as mud brec-cia clasts. They are structureless, massive, usually angular, and forma variety of shapes. Their size range is 1–3 mm.

Polycrystalline aggregates of calcite are mainly angular, strtureless, of various size, and abundant. They are probably fragmof calcite veins from carbonate rocks, which were crushed dumud breccia formation. Quartz grains are prevalent among crystclasts. They vary in shape, size, and roundness. Plagioclase gand potassium-feldspar grains are less abundant and are usuallthan 0.1 mm in size. Altered grains are commonly rounded, whe

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relatively “fresh” grains are subangular. Monocrystals of calcite, rmuscovite, and glauconite grains were also observed. Bioclasts isamples studied are represented only by planktonic foraminifersfragments of their chamber walls, which are usually filled by spar cite.

These main lithological groups of clasts are present in all mbreccia samples, with some rare exceptions that are explained bsmall amount of material available for this study (Table 1). No snificant variations in the mud breccia clast lithology were notdownhole.

Mud Breccia Matrix

Mud breccia matrix consists of clay minerals with an admixtuof fine, silt-sized grains of quartz, calcite, and feldspar.

The matrix clay mineral composition of the buried mud breccsampled during Leg 160 was defined on the basis of X-ray studThe matrix is mainly composed of smectite and mixed-layered (illsmectite with prevalent smectite layers) clay minerals (44%−66%),kaolinite (17%−30%), and illite (14%−30%). No significant varia-tions in clay mineral composition of the matrix were noted downhor between different volcanoes except for one sample (160-979X-1, 20−22 cm) that is composed predominantly of illite (45%) arelatively small amounts of smectite (27%). Our explanation of tcomposition is that a mudstone fragment was probably analyzestead of the matrix sample.

The clay mineral composition of the mud breccia matrix from L160 samples corresponds exactly with the results of matrix stupreviously carried out for the Olimpi Area mud volcanoes from TT3 data (G.G. Akhmanov, unpubl. data) (Table 2).

Angular, fine, silt-sized grains of quartz, calcite, and feldspar pvide a constant admixture to the predominantly clayey matrix ofmud breccia. Moreover, the subdivision of the mud breccia into trix and clasts is subjective because of very poor sorting. No cgranulometric boundary divides matrix from clasts in the mud brcias. All grain-size classes are well represented. This may be

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plained by considering the processes of mud breccia formatioterms of the gradual mechanical and chemical breakdown of clathey are brought to the seafloor from depth.

Mud breccia formation is believed to begin at the depth of theimentary source deposits. A plastic, mostly clayey, sedimentarries is forced up to the seafloor under overpressure. During its upmigration through overlying deposits, it mechanically assimilafragments of rocks that surround the conduit to the seafloor. breccia development continues after deposition on the seafloor wchemical alteration occurs with further disaggregation of claComposition of the mud breccia matrix is changed in time by thesimilation of clasts.

Thin-section investigations of clast-matrix contacts and matexture and composition were conducted to characterize the tecies of different clast types to disintegrate and become incorpoin the matrix.

Soft and plastic mudstone fragments are important in the fotion of the matrix. Transformation of these clasts into matrix mateforms an entire succession. Micrites and fossiliferous micrites participate in matrix formation, although they are more indurathan the mudstones. Siliciclastic rocks can disaggregate and form into matrix as well. Crystalloclasts (quartz grains, feldsgrains, etc.) are generally the result of disintegration of source rthat gradually become incorporated into the matrix. Mineral grbehave in the matrix according to their chemical stabilities. Qugrains that are the most stable remain almost intact, whereas fegrains may be replaced by clay minerals or calcite. Complete repment produces pseudomorphs after feldspar, which may thensolve in the matrix.

According to their behavior in the matrix, the mud breccia clcan be arranged as a series from the least to the most stable: splastic claystones and mudstones, micrites and fossiliferous micsiltstones, sandstones, fragments of calcite crack fillings, feldgrains, mica, calcite grains, chalcedony, polycrystalline qugrains, and monocrystalline quartz grains, respectively. The cositions of mud breccia matrix and enclosed clasts are closely re

Table 1. Mud breccia clasts observed in samples studied.

Note: + = found in sample.

Lithoclasts Crystalloclasts

Core, section, interval (cm) Mudstone

Sandstone with clayey matrix

Sandstone with calcite cement Siltstone

Packed biomicrite Micrite

Fossiliferous micrite Quartz Plagioclase K-feldspar Calcite Bioclasts

160-970A-1H-4, 60-62 + + + + + + + + + + +2H-1, 60-62 + + + + + + + + + + + +7X-1, 23-25 + + + + + + + + + +9X-1, 20-22 + + + + + + + + +13X-1, 10-12 + + + + + + + + + +15X-1, 60-62 + + + + + + + + + + + +18X-2, 60-62 + + + + + + + + +19X-2, 60-62 + + + + + + + +20X-1, 60-62 + + + + + + + + + + +

160-970C-3H-1, 15-17 + + + + + + + + +3H-4, 80-82 + + + + + + + + +

160-970D-1H-2, 20-22 + + + + + + + +4H-2, 24-26 + + + + + + + + + +5H-4, 90-92 + + + + + + +

160-971A-3H-3, 23-25 + + + + + + + + + + + +6X-1, 4-6 + + + + + + + +9X-CC, 9-11 + + + + + + +

160-971B-4H-1, 5-7 + + + + + + + +7X-1, 5-7 + + + + + + + + + +12X-1, 9-11 + + + + + + + + + +16X-2, 19-21 + + + + + + + + + +19X-3, 21-23 + + + + + + + +22X-1, 5-7 + + + + + + + +

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Sedimentary Structures of Mud Volcanic Deposits

Although mud breccia composition does not vary significantlywith depth below the seafloor, its structural diversity as observed inthin section does vary. Three main types of mud breccia were de-scribed according to their structural features. The main sedimento-logical characteristics of the mud breccia types are summarized inTable 3.

1. The most widespread mud breccia type is represented by a verypoorly sorted, matrix-supported, massive, unlayered, ungradedmixture of clay matrix with abundant clasts that vary in compo-sition, shape, size, and roundness. The clast size in the samplesstudied varies from 0.01 to 10 mm, but most clasts are between0.1 and 2 mm in size. Clasts show no preferred orientation. Thematrix consists of calcite, clay minerals, and fine silt-sizedgrains of quartz and feldspar. Mud breccia of this type domi-nates and forms the central parts of mud breccia flows (i.e.,middle parts of individual beds). This type of mud breccia is themost commonly occurring; thus, we refer to it as “ordinary mbreccia.”

2. In contrast to structureless, ordinary mud breccia, a second tymud volcanic deposit is organized. Mud breccia of this tydisplays a preferred orientation of bladed grains. Deformaof soft, plastic fragments of clay and mudstones is commBreccia of this type is associated with the outer extremitiemud breccia flows (i.e., toward the bed contacts). Usually, breccia shows an increase in carbonate content toward thetacts because of partial mixing of adjacent high-carbonateposits. Sorting of this breccia also increases toward the conLarge clasts are almost absent; grains up to 2 mm in size dinate. We use the term “organized mud breccia” for such deits.

3. A third type of mud volcanic facies observed in the samples fLeg 160 may not really be a mud volcano breccia in the s

Table 2. Clay mineral composition of mud breccia matrix sampled dur-ing Leg 160 and TTR cruises.

Note: * = sum of smectite and mixed-layered (illite/smectite) clay minerals with preva-lent smectite layers.

Core, section,interval (cm)

Kaolinite (%)

Illite(%)

Smectite* (%)

160-970A-1H-4, 60-62 22 17 612H-1, 60-62 21 16 637X-1, 23-25 30 21 509X-1, 20-22 28 46 2713X-1, 10-12 20 27 5215X-1, 60-62 24 24 5218X-2, 60-62 19 25 5619X-2, 60-62 22 15 6420X-1, 60-62 21 22 56

160-970C-3H-1, 15-17 20 25 553H-4, 80-82 23 27 50

160-970D-1H-2, 20-22 21 14 664H-2, 24-26 20 30 505H-4, 90-92 18 24 58

160-971A-3H-3, 23-25 24 22 546X-1, 4-6 30 26 44

160-971B-4H-1, 5-7 27 20 537X-1, 5-7 21 21 5812X-1, 9-11 17 25 5816X-2, 19-21 24 24 5219X-3, 21-23 24 23 5422X-1, 5-7 20 25 55

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sense, although it originated from the mud breccia depositstervals of such deposits were interpreted as coarse-grainedbidites during Leg 160 shipboard investigation (EmeRobertson, Richter, et al., 1996). This type of deposits is resented by clast-supported facies that shows fine, planar lamtion. Some samples are graded, and clasts show a preforientation. In contrast to ordinary breccia facies, relativegood sorting is observed, especially in the fine-grained sples. The structural and textural features imply transportaof material by a more liquid gravity flow (i.e., probably a tubidity current) than most common mud breccia flows. Tcomponent composition of the deposits is the same as for tcal ordinary mud breccia. Clasts of all lithologies, describedthe ordinary mud breccia, were observed in samples of thsediments: micrites, fossiliferous micrites, sandstones, cstones, and all types of crystalloclasts. Matrix compositionalmost the same as that of ordinary mud breccia as well. deposits were formed by gravity flows transporting materderived from ordinary breccia. This material was sorted durits transportation and redeposited as local turbidites notfrom a source area (e.g., the mud volcano crater or the uslope of the mud volcano). We refer to these sediments asdeposited mud breccia.” The redeposited mud breccias wdescribed for intervals around 170 m below seafloor (mbsfthe outer flanks of the Milano mud volcano (Hole 970A) athe Napoli mud volcano (Hole 971B). Redeposition of mbreccias in this way might be related to some period of tectoactivity in the area. We must note here that the microstructtypes of mud breccia, proposed above on the basis of thin-tion study of the ODP samples, are different from the litholoical types that were identified by Staffini et al. (1993) on tbasis of the visual description of the Olimpi and Prometheumud breccia.

DISCUSSION

The Olimpi diapiric field was the most studied area of mud volnism on the Mediterranean Ridge, even before Leg 160. Numenational and international expeditions have discovered 23 domestructures there, 16 of which were sampled and found to contain breccia (Fig. 2). Some peculiarities of exposed mud breccia litholfrom this area were described in a series of publications (Cita e1989; Camerlenghi et al., 1992; Staffini et al., 1993; Cita et al., 19Akhmanov, 1996; Premoli-Silva et al., 1996; van der Meer, 199ODP samples have given us a unique opportunity to investigatenature of buried mud breccia flows, thus providing data on posstime variations in mud volcanism.

The composition of buried mud breccias recovered during L160 were found to be rather typical of the Olimpi area as determfrom earlier studies. That significant differences from mud brecexposed on the seafloor were not observed is an important resthis research. Most of the lithoclast types previously described forposed mud breccia flows of the Olimpi area were found in the Osamples. No new types were observed in the buried older mud bcia. The approximate percentage composition of mud breccia deits from both the ODP and other data sets is almost the same.

Table 4 summarizes the comparison between the lithoclastsserved in ODP samples from buried mud breccia and the typerock fragments previously described for the Olimpi mud breccia posed on the seafloor. The two sets of lithoclasts and their litholoare almost identical.

Mudstone is prevalent among the clasts of the mud breccia sples recovered by ODP, as well as in Olimpi mud breccia sampreviously by seafloor coring operations. Micrites and fossiliferomicrites are as widespread among lithoclasts of the limestone g


Table 3. Sedimentological characteristics of the Olimpi area mud breccia sampled from Leg 160 by definition in thin section.

“Ordinary” mud breccia “Organized” mud breccia “Redeposited” mud breccia

Structure Massive Massive Finely planar laminated or gradedFabric Matrix-supported Matrix-supported Clast-supportedSorting Very poorly sorted From poorly to well sorted towards contacts Moderately sortedClast orientation No orientation Preferred orientation of bladed grains No orientationPosition Inner part of mud breccia flow Upper and lower parts of mud breccia flows Outer flanks of mud volcanoes

Mud breccia of inner part of flow Mud breccia of upper or lower parts of flow Local gravity flows from crater or upper slope of mud volcano

101

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150 200 250 300

400

350

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33 400

33 500

MEDITERRANEAN

RIDGE

Figure 2. Location of the mud volcanoes of the Olimpi/Prometheus 2 Area, surveyed during Cruise TTR 3, Leg 2 (after Cita et al., 1996).

as in the youngest mud breccia flows. Packed biomicrites were ob-served among the mud breccia clasts in the samples collected duringthe TTR-3 expedition and in the Leg 160 samples as well. The differ-ent sandstone fragments observed in the ODP mud breccia samplescorrespond to the subfeldspathic lithic wackes and lithic arenites pre-viously described for the Olimpi area where larger clasts of theserocks were sampled (Akhmanov, 1996). Sedimentary structures ofthe sandstones have suggested turbiditic origin and deep-sea environ-ments: graded bedding, convoluted lamination, low-angle micro-cross lamination, gradual transition into siltstones, and other geneticindications (Akhmanov, 1996).

The only limestone type observed in the previously analyzed mudbreccia clasts from the Olimpi area, but not observed in the Leg 160samples of the buried mud breccia flows, were fragments of pel-

sparite. Pelsparites are not widespread rocks. Usually, they form rath-er thin layers interbedded with other types of limestone.

Fragments of pelsparites are the rarest among the clasts from theOlimpi mud breccia (less than 1%) and were recorded only for theToronto and Moscow mud volcanoes (Table 3), although large vol-umes of material from different volcanoes of the Olimpi area wereexamined (Akhmanov, 1996). The relatively small volume of theODP samples might have been insufficient for observation of suchrare clasts.

The crystalloclasts have all resulted from disintegration of differ-ent rock fragments within the mud breccia. The set of crystalloclastscorresponds completely to component compositions of the litho-clasts. Quartz grains, plagioclase grains, potassium-feldspar grainsand muscovite are from the subfeldspathic lithic wackes and the lithic

601


602

Table 4. Distribution of the main mud breccia clast types among the Olimpi Area mud volcanoes.

Note: + = present. ODP Leg 160 is shown in comparison with TTR data.

TTR data (after Akhmanov, 1996) Leg 160 samples

Moscow Stvor Maidstone Milford Haven Leipzig Jaen Gelendzhik Toronto Napoli Milano

Packed biomicrites (5%) + + + + + + +Micrites (15%) + + + + + + + + +Fossiliferous micrites (10%) + + + + + + + + + +Crystalline limestones (4%) + + + + + + + +Pelsparites (1%) + +Subfeldspathic lithic wackes (6%) + + + + + + + +Lithic arenites (4%) + + + + + + + + +Siltstones (5%) + + + + + + + + + +Mudstones (50%) + + + + + + + + + +

arenites. Monocrystals of calcite are from the rocks of the limestonegroup, or originate as fragments of calcite cement from the lithicarenites. The crystalloclasts observed in the mud breccia samples areusually less than 0.25 mm and never more than 0.5 mm in size. Thiscorresponds to the grain-size parameters of the lithoclasts describedfor the Olimpi mud breccia (Akhmanov, 1996).

Bioclasts in mud breccias probably result from disintegration ofrock fragments within mud breccia, like the other clasts. Most of thebioclasts are from carbonate rocks rich in skeletal components. Somemay be from lithic arenites (Akhmanov, 1996).

Some results of microscopic study of the mud breccia samples areshown in Figures 3 and 4, which illustrate the lack of regular varia-tion in the mud breccia clast composition with depth in Hole 970Afrom the Milano mud volcano and in Hole 971B from the Napoli mudvolcano, respectively. Absence of some clast types in some samplesmay be explained by the limited volume of mud breccia sampled onLeg 160, which was insufficient for complete observations of thesuite of clasts known to be present from previous studies. No regularvariation in the mud breccia clast lithology was noted for the Leg 160samples. Clay mineral composition of the mud breccia matrix doesnot vary significantly downhole at either the Leg 160 Milano orNapoli mud volcano sites (Figs. 5, 6).

Examination of the Olimpi mud breccia on the basis of the ODPdata shows a lack of significant downhole variation in mud brecciamatrix and clast composition. This suggests that the source forma-tions for the mud breccia of the Olimpi Area mud volcanoes have notchanged since at least the late Pliocene.

We discussed above the results of the lithological study of themud breccia from the Olimpi diapiric area only. It is also of value tocompare the findings from this particularly well studied mud diapiricfield, the Olimpi Field, with results from other areas of mud volca-nism along the Mediterranean Ridge. This is especially important toeventually determine variations in geological setting, includingsource rock variation, and different stress regimes along the Mediter-ranean Ridge, from compression in the center and west to transpres-sion in the east.

Even very preliminary lithological comparison of the mud brec-cias sampled from the Olimpi area with those from other known dia-piric areas on the Mediterranean Ridge has shown distinct character-istics for each area of development of mud volcanism. The mud brec-cia of the Cobblestone 3 diapiric area on the western part of theMediterranean Ridge is different from the Olimpi mud breccia. Veryspecific fragments of detrital limestone with a large amount of terrig-enous constituents, reddish brown mudstone, and siderite aggregatewere obtained from the mud breccia clasts from the Aros and No-vorossiysk mud volcanoes, and from an unnamed mud volcano (Fig.1). Clay mineral composition of the matrix differs slightly as well.

Napoli mud volcano (Hole 971B)

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LEGEND: - pelagic sediments - mud volcanic deposits

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Figure 3. The Napoli mud volcano. Figure shows downhole variation of mudbreccia clast composition. Lithology, core recovery, and age information ofHole 971B are adapted from Emeis, Robertson, Richter, et al. (1996).


Although recently discovered mud volcanoes of the United Na-tion Rise diapiric area are located relatively close to the Olimpi Area,the lithology of their mud breccias was found to have many specificfeatures. Light-gray subarkose sandstones, gray bioclastic lime-stones, and grayish brown mudstones observed in mud breccia sam-ples collected from the Stoke-on-Trent and Dublin mud volcanoes(Fig. 1) were not noted before for other areas of mud volcanism onthe Mediterranean Ridge (Cronin et al., 1997).

The specificity of the composition of the mud breccia from differ-ent mud volcanic areas of the Mediterranean Ridge reflects peculiar-ities of source formation lithology and structural tectonic setting ofmud volcano roots that are different in different areas of the EasternMediterranean. Some common features of the Mediterranean mudbreccia lithology were also found. Fragments of dark-gray mudstone,

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Figure 4. The Milano mud volcano. Figure shows downhole variation of mudbreccia clast composition. Lithology, core recovery, and age information ofHole 970A are adapted from Emeis, Robertson, Richter, et al. (1996).

light-gray micritic limestone, light yellowish gray marlstone, andlight-gray fossiliferous micrite were found in most of mud brecciasamples from different areas. Moreover the fragments of these rocksare often prevalent among the lithoclasts, probably corresponding tocommon sedimentary series widespread in the subsurface of thewhole Eastern Mediterranean.

CONCLUSIONS

The most important findings of the study performed on the ODPsamples from the Olimpi mud breccia and their comparison with theprevious data may be summarized as follows:

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Figure 5. The Napoli mud volcano. Figure shows downhole variation of claymineral composition of mud breccia matrix. Lithology, core recovery, andage information of Hole 971B are adapted from Emeis, Robertson, Richter,et al. (1996).

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1. The composition of buried mud breccia flows recovered fromthe Leg 160 sites is similar to that of samples from other partsof the Olimpi area. The lack of significant differences in thecompositions of the mud breccia exposed on the seafloor andthe buried mud breccia recovered at the ODP sites suggeststhat the source series for the Olimpi mud breccia have notchanged since at least the late Pliocene.

2. The structural diversity of mud volcanic deposits with depth asobserved in thin section can be classified according to the mi-crostructural features into three main types of mud breccia: themost widespread structureless “ordinary mud breccia,” whforms the central parts of flows (i.e., middle parts of individ

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Figure 6. The Milano mud volcano. Figure shows downhole variation of claymineral composition of mud breccia matrix. Lithology, core recovery, andage information of Hole 970A are adapted from Emeis, Robertson, Richter,et al. (1996).

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beds); the “organized mud breccia” associated with the ouparts of mud breccia flows (i.e., near the upper or lower ctacts); and the “redeposited mud breccia” formed by gravflows transporting reworked ordinary breccia as local turbites not far away from the mud volcano.

3. The composition of the mud breccia from different mud volcnic areas known along the Mediterranean Ridge reflects peliarities and variability of the source formation lithology anstructural tectonic setting in different parts of the Eastern Meiterranean. Nevertheless, some common features of the Mterranean mud breccia may correspond to sedimentary sethat extend throughout the entire Eastern Mediterranean.

ACKNOWLEDGMENTS

The authors wish to thank the Netherlands Foundation for EScience for contributions to the TTR Programme and for supporJohn Woodside in his participation in Leg 160. We wish to exprour appreciation to UNESCO, IOC, European Science FoundatRussian Committee for Geology, and national funding organizatof the Russian Federation, the Netherlands, United Kingdom, analy for the financial support and encouragement of the TTR Pgramme. Our thanks are extended to the crews and technical stathe research vessels Gelendzhik and Professor Logachev and thedrilling vessel JOIDES Resolution for their excellent contribution tothe success of the cruises. Personal thanks are addressed to DrLuksha, Dr. V.L. Kosorukov, R.M. Almendinguer, and S.V. Bouria(Moscow State University) for scientific and technical support of tX-ray studies and to P.V. Shashkin for help in preparation of thelustrations. Reviews by Professor M.B. Cita, Dr. B.T. Cronin, andanonymous reviewer are gratefully acknowledged. The first autwould like to thank Dr. M.K. Ivanov and Dr. A.F. Limonov for encouragement to perform the present study and for providing contous scientific support.

REFERENCES

Akhmanov, G.G., 1996. Lithology of mud breccia clasts from the Mediterra-nean Ridge. Mar. Geol., 132:151−164.

Camerlenghi, A., Cita, M.B., Della Vedova, B., Fusi, N., Mirabile, L., andPellis, G., 1995. Geophysical evidence of mud diapirism on the Mediter-ranean Ridge accretionary complex. Mar. Geophys. Res., 17:115−141.

Camerlenghi, A., Cita, M.B., Hieke, W., and Ricchiuto, T.S., 1992. Geologi-cal evidence for mud diapirism on the Mediterranean Ridge accretionarycomplex. Earth Planet. Sci. Lett., 109:493−504.

Cita, M.B., Camerlenghi, A., Erba, E., McCoy, F.W., Castradori, D., Cazzani,A., Guasti, G., Giambastiani, M., Lucchi, R., Nolli, V., Pezzi, G.,Redaelli, M., Rizzi, E., Torricelli, S., and Violanti, D., 1989. Discovery ofmud diapirism in the Mediterranean Ridge: a preliminary report. Boll.Soc. Geol. Ital., 108:537−543.

Cita, M.B., Ivanov, M.K., and Woodside, J. (Eds.), 1996. The MediterraneanRidge diapiric belt: introduction. Mar. Geol., 132:1−6.

Cita, M.B., Ryan, W.B.F., and Paggi, L., 1981. Prometheus mud-breccia: anexample of shale diapirism in the Western Mediterranean Ridge. Ann.Geol. Pays Hellen., 30:543−570.

Cita, M.B., Woodside, J.M., Ivanov, M.K., Kidd, R.B., Limonov, A.F., andScientific Staff of Cruise TTR3 Leg 2, 1994. Fluid venting, mud volca-noes and mud diapirs on the Mediterranean Ridge. Rend. Fis. Acc. Lin.Roma, 5:161−169.

Cronin, B.T., Ivanov, M.K., Limonov, A.F., Egorov, A., Akhmanov, G.G.,Akhmetjanov, A.M., Kozlova, E.V., and Shipboard Scientific Party TTR-


3, 1997. New discoveries of mud volcanoes on the Eastern MediterraneanRidge. J. Geol. Soc. London, 154:173−182.

Emeis, K.-C., Robertson, A.H.F., Richter, C., et al., 1996. Proc. ODP, Init.Repts., 160: College Station, TX (Ocean Drilling Program).

Limonov, A.F., Woodside, J.M., Cita, M.B., and Ivanov, M.K., 1996. TheMediterranean Ridge and related mud diapirism: a background. Mar.Geol., 132:7−19.

Premoli-Silva, I., Erba, E., Spezzaferri, S., and Cita, M.B., 1996. Age varia-tion in the source of the diapriric mud breccias along and across the axisof the Mediterranean Ridge Accretionary Complex. Mar. Geol.,132:175−202.

Staffini, F., Spezzaferri, S., and Aghib, F., 1993. Mud diapirs of the Mediter-ranean Ridge: sedimentological and micropalaeontological study of themud breccia. Riv. Ital. Paleontol. Stratigr., 99:225−254.

van der Meer, R., 1996. Grading in mud volcanic breccia from the Mediterra-nean Ridge. Mar. Geol., 132:165−173.

Date of initial receipt: 7 February 1997 Date of acceptance: 5 September 1997 Ms 160SR-045

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